1. Field of the Invention
The present invention relates to a coupler for managing communication between a portable data medium and a data exchange device, which communication uses, on the data exchange device end, at least one data transmission signal and two control V signals delivered by the data exchange device in one of two first and second predetermined input sequences, and on the data medium end, at least one data medium power supply signal, one data medium reset signal, and one data transmission signal.
This coupler can be used for example to limit access to a computer network to authorized persons who hold for this purpose a portable data medium such as a chip card incorporating a microprocessor or micro-wired logical circuits which define areas to which access is controlled and can therefore contain secret information such as cryptographic keys (see for example the portable object described in U.S. Pat. No. 4,211,919).
2. Description of Related Art
The protocol for data exchange with a chip card is codified by international standard ISO7816-3, which defines the sequence for generating the signals applied to the chip card, namely a power supply signal VCC, a power supply signal for the memories VPP, a reset signal RST, a clock signal CLK, and a data exchange signal I/O. The standard very precisely defines the order in which these signals must appear and then disappear.
A coupler of this type can, in a known way, comprise a microprocessor which controls the interface with the portable data medium and is controlled by the data exchange device which constitutes the central processor. This microprocessor slows down the exchange process between the asynchronous data exchange device and the portable data medium.
In order to avoid the use of a microprocessor in the coupler, it has been suggested that some of the signals supplied by a serial port of the data exchange device, typically a port according to the standard RS 232, namely a "clear to send" signal CTS, a request to send signal RTS, a "data carrier detect" signal DCD, a "data terminal ready" signal DTR, a data transmission signal TX and a data reception signal RX, be used to generate the signals applied to the portable data medium.
A coupler of this type is described in U.S. Pat. No. 5,149,945. The sequencing of the signals supplied to the chip card is defined exclusively by the data exchange device, without the coupler's being able to intervene in this sequencing so as to allow for particular operating situations on the chip card end.
One consequence is that the above-mentioned standard is not always met, particularly when the chip card is reinserted after having been removed during a communication with the data exchange device, since the chip card is powered up again immediately, without allowing the data exchange device the necessary time to react in so as to impose a re-powering up in accordance with the standardized sequence.
However, it appears to be desirable for the coupler to be able to intervene in the sequencing of the signals delivered by the data exchange device in order to supply a wider range of modes for controlling or testing the chip card.